Highly-flexible pressure-sensitive adhesive tapes may be used typically as protective tapes upon processing of steel sheets or plates. As such highly-flexible pressure-sensitive adhesive tapes, Japanese Unexamined Patent Application Publication (JP-A) No. 2007-314636 (PTL 1) discloses a pressure-sensitive adhesive tape including a poly(vinyl chloride) film (PVC film) as a base material (substrate). The PVC film substrate contains bis(2-ethylhexyl)phthalate (DOP or DEHP) or dibutyl phthalate (DBP) as a plasticizer.